The present invention relates to a gravity feed roller conveyor and more particularly to a roller conveyor that accumulates or holds pallets or in a buffer zone immediately adjacent an end position where the products are used.
In conventional assembly operations, parts to be assembled are placed on pallets and then pallets are placed on conveyors leading to assembly stations where the parts are used. The length of conveyor upstream from the assembly location is deemed to be a “buffer” zone, wherein a supply of parts is maintained for use at the assembly point. In some operations, these buffer zones comprise a downwardly inclined conveyor that leads from an upper loading area downwardly in spiral fashion through a series of inclined straight sections, connected together by arcuate sections that extend through horizontal angles or bends of 30°, 45°, 90°, or 180°, until the parts reach the bottom of the conveyor, wherein the assembly station is located. Most such conveyors are driven conveyors, wherein a conveyor belt or conveyor chain for each conveyor section is driven by a motor and gears in an endless loop path, and adjacent sections of driven chain are positioned end to end with respect to each other. Where conveyors are driven around arcuate bends, it is conventional to use an articulating conveyor chain, wherein a plurality of longitudinally spaced links having arcuate adjoining edges are pivotally connected together so as to permit the chain to follow an arcuate horizontal path.
When the chain is used to provide a buffer zone in an accumulating conveyor (where the products stop but the chain keeps moving), the stopped products create drag on the moving chain. Low friction links reduce friction stress, but heavy products make friction a problem. To minimize this problem, a different type of drive chain, called “roller top chain” can be used. Roller top chain includes rollers mounted on the tops of the links, so that when the products are stopped, the conveyor can continue to move underneath the products, with the conveyor rollers rolling underneath the products as the links continue to move in an oval path under the products.
A serious problem with driven accumulating or buffer conveyors of this nature is that the weight of the products on the links causes a great deal of wear on the various moving mechanisms of the system, as well as on the drive components of the system. Replacement parts are expensive, and maintenance and repair of such systems involves a substantial amount of down time for the assembly line.
In driven systems of the type described above, it is conventional to position the straight sections of track at an inclined angle but to position the arcuate portions of the conveyor at the ends of the straight sections in a horizontal plane, with a rotatable horizontal bend wheel being on the inside of the bend. The horizontal orientation of the bend sections causes the products to stack up in the bend sections. This increases the load and wear on the system substantially.
An object of the present invention is to provide an improved accumulating conveyor system that can easily be used in existing conveyor systems without the maintenance problems and down time associated with conventional driven conveyor systems.